I think every game had their pros and cons for me, so it's hard to say whether or not I truly despised a certain one...
R/B/Y were the ones that got me into Pokémon in the first place, and while I don't remember exactly how I felt about then when I was playing them (since it was 10+ years ago), they must have been good. If they weren't, I wouldn't have continued playing. :P
I missed out on G/S/C.
R/S/E are alright, but it's definitely one that I try to avoid playing unless I have to. I'd still like to go back and get all of the legendaries to transfer over to my Platinum, but...I dunno, there's just something about it that keeps me away.
I didn't play FR/LG either...
Pearl was the one that got me back into Pokémon, so I like it in that aspect. Platinum is my meta-cartridge that holds all of my treasured Pokémon, has the most hours, and so on. Pearl was just so incredibly painstakingly slow from the gameplay mechanic perspective. It was really frustrating to take 30 seconds just to start a stupid battle.
SoulSilver's alright, but the storyline felt really rushed. All of the gym leaders were defeated only about 50 hours in, and I'm having trouble finding the motivation to level grind so I can defeat Red. I'd probably have more fun with it if I originally played G/S/C.
Hey You Pikachu wins my vote for worst spin-off. It was pretty much an expensive waste of time :/